An uncooled infrared imaging element generally passes a constant forward current through a diode-array to serve as heat-sensitive pixels provided on a Si substrate to detect dVf/dT which is a change in a forward voltage Vf with temperature. The change is a weak signal having several microvolts. Therefore, two or more diodes are series-connected to increase the signal intensity, thereby enhancing a signal-to-noise ratio. This requires voltage driving to be proportional to the number N of diodes so that a voltage of about 10V is applied between the source and drain thereof.
However, there has been a problem that previous uncooled infrared imaging elements could involve a leak current of source-to-drain in some cases. The leak current is caused by applying a high voltage to an SOI transistor included in the element. In the high-voltage applied SOI transistor, an SOI supporting substrate and BOX of the element can serve as a gate and a gate insulator film, respectively, to produce an inversion layer (back channel) at the interface between the gate and the gate insulator. The inversion layer can cause the leak current.